How to calibrate a grain drill

For farmers looking to diversify in 2017, oats and spring wheat are two good options. While prices are low across the board for commodities, growing small grains in Iowa can help reduce input costs. By disrupting weed cycles with a cool-season crop like oats or wheat, farmers can save money on herbicides.

Underseeding the crops with a green manure like red clover or drilling a multispecies cover crop mix after the small-grain harvest are ways farmers can save money on fertilizer. That same multispecies mix can include both legumes for nitrogen fixation and productive forages like sorghum sudangrass, which can be grazed in the winter and provide savings on hay.

The time to plant small grains is rapidly approaching, and a little planning now can make a big difference in yield when it comes time to harvest in July.

Wade Dooley of Albion in central Iowa grows small grains like rye and oats for cover crop seed and uses the straw in his cattle feedlot. Since he began growing small grains a few years ago, he pays attention to more details in order to boost grain quality and yield. Among these important details are variety selection, fertility and crop protection, and planting populations.

“You wouldn’t go out and plant corn without making sure your planter is behaving properly,” he says. Dooley calibrated his drill to plant rye last fall and will do the same for planting oats this spring.

Seed size variesFirst, he counted 1,000 seeds, which gives a pretty accurate sample size of a given seed lot. A smaller number, like 100, could give an unreliable representation of the seed size, and counting more than 1,000 is unnecessary in most cases. Stefan Gailans, research and field crops director for Practical Farmers of Iowa, has a helpful blog on the PFI website about how much seed size can change planting rates.

“It’s slow and it’s tedious. It took about 20 minutes to count out the 1,000 seeds. But it’s really important so that we get our calibration right for our planting population,” Dooley says. As luck would have it, those 1,000 seeds that he counted out weighed exactly 1 ounce, meaning that a pound of seed from that lot contained 16,000 seeds. Seeds for small grains can vary widely in size, with a pound of seed containing anywhere from 12,000 to 17,000 seeds, depending on variety and lot.

Once you know the weight of the seed (the number of seeds per pound), you can figure out a good seeding rate for your target planting population. What is that population? It depends on the crop and variety, but the latest recommendations from Iowa State University are somewhere between 1 million to 1.3 million plants per acre for oats. Recommendations from University of Minnesota hover in the upper end of that range, and Grain Millers, who mills oats in St. Ansgar in northeast Iowa, advises toward the lower end.

If you’re planning on making small grains on a part of your farming operation, the rate itself is probably less important than knowing the rate you actually planted, so you can modify in the future based on what works for your farm. And to do that, you have to calibrate your grain drill.

Planting population for small grainsTo get at that desired plant stand, you need to also figure in stand loss and germination rate, and you can do that using the following formula.

Let’s use Dooley as an example. He got his winter rye planted early, so he went for a lower rate because he knew it would have time to establish well and tiller. This would probably be a bit too low of a population for oats, especially if you were getting them in late. He wanted somewhere around 800,000 to 900,000 plants per acre at harvest. We’ll figure his stand loss at 15% (10% to 20% is a good estimate), and his germination rate at 95%.

850,000 / 0.85 = 1,000,00016,000 x 0.95 = 15,2001,000,000/15,200 = About 65 pounds or a little over a million seeds per acre

Seeding what you want to seedNow that you’ve got your target seeding rate, it’s time to make sure your drill is putting that amount out. When it comes to adjusting the grain drill to change the seeding rate, Dooley says you can look at the chart usually printed on the inside of the box lid or the owner’s manual for starters, but those are pretty generic. “Those are for ‘guesstimated’ seed sizes,” he says. “Every seed lot is going to be different, just like corn and soybeans. One batch of seeds may be slightly different sized than the other, and that can really affect how your drill operates.”

Most drills will have a process for calibration in the owners’ manual, but if yours doesn’t, you can figure it out yourself. There are several different ways of doing this, but basically, you’re going to weigh the amount of seeds you put out over a given area. If you’re going to be doing this in February before oat planting in March, this is probably most easily done in the shop.

Since you already know the number of seeds in a given weight, what you need is to simulate seeding a known area. The easiest way to do this is to unhook the tubes from the slots on the grain box and put a bag or bucket underneath those openings to catch the seed, jack up the drill, and turn the drive wheel a few times to meter the seed out. You can then weigh that seed. To know how far you “went” and the area you “seeded,” you need to know the circumference of the drive wheel, the drill row spacing, the number of tubes you caught seed from, and the number of times you turn the wheel.

Thus, the area he simulated the seeding over was about 308 square feet, or 0.0071 acres. He weighed the seed and recorded 4.5 ounces, or 0.28 pound.

Scaling up the ratio of 0.28 pound over 0.0071 acre to a whole acre gives us 39.44 pounds per acre. Since he already counted the number of seeds per pound and knew there were about 16,000 per pound in this given lot, he could figure that his drill was seeding at just over 600,000 seeds per acre. But remember, he was shooting for just over a million for a seeding rate. Because he was low, he opened up the seed meters accordingly, turned out some more seeds, and got the rate up to where he wanted it. That’s all there is to it.

For more information on small-grain production, check out PFI’s new video series, Rotationally Raised on YouTube.